The production of tubes of glass or other types of containers obtained from glass tubes, according to the state of the art, is particularly relevant owing to the many critical applications where they are used, particularly in the health industry.
Among the many articles that are industrially produced starting from a glass tube, for example, containers can be cited used in the pharmaceutics industry such as vials, ampoules, cartridges, syringes, as well as laboratory apparatus, such as graduated cylinders, pipets, burets, refrigerants, etc., adopted in chemical laboratories.
In the industrial field, a raw glass tube has to comply with particular quality regulations and predetermined dimensional characteristics before being allowed on successive production lines.
For example, the pharmaceutical industry demands glass tubes which meet particular requirements, and, in particular, a high chemical stability, a low thermal expansion coefficient (which makes it resistant to relevant temperature changes), and strictly controlled dimensional characteristics, in order to ensure maximum quality and production efficiency for the above described products. In particular the glass has to be free from fragments or particles both on its outer surface and especially on its inner surface. For most uses in the pharmaceutical field, glass containers shall contain “no particles”, and the producers have to assure absence of particles from the products.
However, the production process for the tubes involves necessarily generation of fragments, for the peculiar nature of the material and, in particular, owing to the various cut and work operations made on glass.
In more detail, after hot forming downstream of the oven, the glass tube is cut a first time at a length not much longer than the final use. The cutting equipment is a rotating device, synchronised with the glass tube drawing speed, which causes the continuous tube to be cut in a cutting point by a rotating blade.
A further cutting step is done on both ends of the tube up to refine the cut and to obtain the final desired length with the desired tolerances.
The above described cutting steps generate fragments and/or particles that can adhere outside or within the tube. Even other events where freshly cut surfaces are involved, are potential sources of contaminating particles such as, for example, the contact with conveying guides or aligning wheels or other parts of the machines or the packages.
The production process comprises, before packaging or storing the tube as semifinished product, at least one process step dedicated to extract glass fragments or other particles from the inside of the tube.
The fragments or particles that adhere on the outer surface can be easily removed with brushing, washing or jets of air. The removal of those that adhere on the inner surface, instead, cannot be obtained with the same ease.
According to the prior art, the extraction step of the fragments or particles that adhere on the inner surface of the tubes uses a fluid jet, such as air, with a determined speed, directed into the tubes for eliminating the stuck fragments.
It must be noted that, in case of failure or incomplete effectiveness of the extraction step, the final requirements of the product are not met, especially in the pharmaceutical industry, in that the fragments, because of the peculiar hardness, brittleness and sharpness of glass, are a potential source of highly harmful consequences and certainly cannot be accepted in a container for injectable preparations.
To overcome this disadvantage, further steps of inspection and selection, and measures such as washing steps are carried out on the finished containers before the filling process, and the products that are out of quality ranges follow further treatments or analysis, or are rejected, thus affecting in both cases the costs and the production time.
Furthermore, a complementary limitation to the above described cleaning operations occurs when standard containers are produced and sold closed and ready to the use. These containers, such as in particular “D-form” ampoules or RTF® syringes (Ready To Fill), are conceived for a direct filling without washing and are therefore required to meet the highest quality requirements, in particular the absolute absence of fragments and/or particles already when they exit from the first production line.
Among the drawbacks concerning the extraction step described above, this method can eliminate only one part of the fragments, leaving a remaining amount of fragments still stuck to the container. This is due, mainly, to the fact that they adhere to the inner surfaces of the tube by means of electrostatic forces that an air jet cannot overcome. Such forces are due to presence of electric charges on the fragments and/or particles at the end of the tube manufacturing steps and particularly after the cutting process.
Various systems are known for reducing or eliminating the electrostatic forces that may cause fragments to adhere to the inner surfaces of containers, by using ionized air.
US2007240784A1 and US2003115710A1 describe a method adapted to remove particles from bottles of plastics that are arranged upside-down. A jet of ionized air enters the bottles, and then a jet of normal air follows to remove the particles. This method is not suitable for glass tubes, which are long and cannot proceed vertically.
U.S. Pat. No. 3,071,497A describes a method adapted to remove particles from glass containers like ampoules vials, syringes, cartridges, used for containing drugs and pharmaceutical products. The method provides blowing externally a jet of ionized air and then applying a mechanical vibration to the container that is oriented with its mouth towards below, so that the particles may fall by gravity. Also in this case the method is not adapted for long glass tubes, like those object of the present application. Also in case of short glass tubes, or container made by glass tubes, the method of U.S. Pat. No. 3,071,497A cannot be used, owing to the very strict requirements concerning fragments or particles.